Internal combustion engine

ABSTRACT

An internal combustion engine according to the present invention includes an exhaust treatment apparatus provided in an exhaust passage, and a burner apparatus provided upstream of the exhaust treatment apparatus to raise exhaust temperature. A valve driving state of at least one of an intake valve and an exhaust valve is controlled so as to reduce a flow rate of exhaust gas passing through the burner apparatus when the flow rate of the exhaust gas is equal to or larger than a predetermined value. Possible flame blow-out in the burner apparatus can be prevented or suppressed to ensure sufficient ignition performance.

TECHNICAL FIELD

The present invention relates to an internal combustion engine, and inparticular, to an internal combustion engine with a burner apparatusprovided in an exhaust passage and upstream of an exhaust treatmentapparatus to raise exhaust temperature.

BACKGROUND ART

In some internal combustion engines, a burner apparatus is provided inan exhaust passage and upstream of an exhaust treatment apparatus(catalyst). Heated gas generated by the burner apparatus is utilized toraise exhaust temperature to heat the exhaust treatment apparatus, thusfacilitating warm-up of the exhaust treatment apparatus.

PTL1 discloses a catalyst temperature rise apparatus including anaddition valve that allows fuel to be injected and ignition means with aheating section that allows the injected fuel to be ignited. Theaddition valve and the ignition means are disposed at such positionsthat allow the fuel injected through the addition valve to come intodirect contact with the heating section. Thus, typically, the burnerapparatus uses the appropriate ignition means to ignite and combust thefuel injected into the exhaust passage.

The ignition performance of the burner apparatus tends to be degradedwhen the flow rate of exhaust gas passing through the burner apparatusincreases to or beyond a predetermined value. This is because at theincreased flow rate, the exhaust gas may blow out the flame, making theignition difficult.

Thus, an object of the present invention is to provide an internalcombustion engine that allows sufficient ignition performance to beensured even when the flow rate of exhaust gas passing through theburner apparatus increases.

CITATION LIST Patent Literature

PTL1: Japanese Patent Laid-Open No. 2006-112401

SUMMARY OF THE INVENTION

An aspect of the present invention provides an internal combustionengine characterized by including:

an exhaust treatment apparatus provided in an exhaust passage;

a burner apparatus provided upstream of the exhaust treatment apparatusto raise exhaust temperature, and

valve driving control means for controlling a valve driving state of atleast one of an intake valve and an exhaust valve so as to reduce a flowrate of exhaust gas passing through the burner apparatus when the flowrate of the exhaust gas is equal to or larger than a predeterminedvalue.

When the valve driving state is thus controlled so as to reduce the flowrate of the exhaust gas, possible flame blow-out can be prevented orsuppressed to ensure sufficient ignition performance.

Preferably, the valve driving control means includes:

a valve timing varying mechanism adapted to vary a valve timing for theexhaust valve, and

first control means for controlling the valve timing varying mechanismin such a manner that the exhaust valve is kept open until during adescent of a piston after end of an exhaust stroke, when the flow rateof the exhaust gas is equal to or larger than the predetermined value.

When the exhaust valve is kept open until during the descent of thepiston after the end of the exhaust stroke, a negative pressuregenerated during the descent of the piston can be utilized to suckexhaust gas back into a combustion chamber. This enables a reduction inthe flow rate of exhaust gas fed to the burner apparatus. Hence,sufficient ignition performance can be suitably ensured.

Preferably, the valve driving control means includes a halting mechanismadapted to halt operation of at least one of the intake valve and theexhaust valve in a part of a plurality of cylinders and second controlmeans for controlling the halting mechanism so as to halt the operationof at least one of the intake valve and the exhaust valve in the part ofcylinders, when the flow rate of the exhaust gas is equal to or largerthan the predetermined value.

When the operation of the at least one of the intake valve and theexhaust valve is halted in the certain number of cylinders, exhaust gasis prevented from being passed from these cylinders toward the burnerapparatus, enabling a reduction in the total flow rate of exhaust gasfrom all the cylinders. Hence, sufficient ignition performance can besuitably ensured.

Preferably, the internal combustion engine further includes detectionmeans for detecting an amount of intake air as a substitute value forthe flow rate of the exhaust gas, and

the valve driving control means controls the valve driving state of atleast one of the intake valve and the exhaust valve so as to reduce theflow rate of the exhaust gas when the amount of intake air detected bythe detection means is equal to or larger than a predetermined value.

Preferably, the burner apparatus includes a fuel addition valve,ignition means, and a pretreatment catalytic converter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of the present invention;

FIG. 2 is a side profile showing a burner apparatus;

FIG. 3 is a front profile of the burner apparatus as seen from anupstream side;

FIG. 4 is a schematic diagram showing that an exhaust valve is closed ina delayed manner; and

FIG. 5 is a schematic diagram showing that operations of an intake valveand the exhaust valve are halted.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of the present invention will be described belowin detail. However, it should be noted that the embodiments of thepresent invention are not limited to those which are described below andthat the present invention includes any variations and applicationsembraced in the concepts of the present invention defined by the claims.The dimensions, materials, shapes, relative arrangements, and the likeof components described in the embodiments are not intended to limit thetechnical scope of the present invention thereto unless otherwisespecified.

FIG. 1 shows an engine main body 1 and an intake and exhaust systemthereof according to an embodiment. The engine main body 1 is an onboardfour-stroke diesel engine. An intake pipe 2 and an exhaust pipe 3(exhaust passage) are connected to the engine main body 1. An air flowmeter 4 is provided in the middle of the intake pipe 2 and outputs asignal corresponding to the flow rate of intake air flowing through theintake pipe 2. The air flow meter 4 detects the amount of intake airflowing into the engine main body 1 per unit time (that is, the flowrate of intake air). The engine main body 1 includes a plurality ofcylinders each including an intra-cylinder fuel injection valve 9.However, FIG. 1 shows only a single intra-cylinder fuel injection valve9.

The exhaust pipe 3 is connected to a muffler (not shown in the drawings)at a terminal thereof and is open to the atmosphere at an outlet of themuffler. In the middle of the exhaust pipe 3, an oxidizing catalyticconverter 6 and an NOx catalytic converter 26 are arranged in this orderfrom the upstream side in series.

The oxidizing catalytic converter 6 allows an unchanged component suchas HC or CO to react with O₂ to obtain CO, CO₂, H₂O, or the like. Acatalytic substance may be, for example, Pt/CeO₂, Mn/CeO₂, Fe/CeO₂,Ni/CeO₂, or Cu/CeO₂.

An NOx catalytic converter 26 preferably includes an NOx storagereduction (NSR) catalytic converter. The NOx catalytic converter 26 hasa function to absorb NOx in inflow exhaust when the exhaust has a highoxygen concentration and to reduce the absorbed NOx when the oxygenconcentration of the exhaust decreases and when a reduction component(for example, fuel) is present. The NOx catalytic converter 26 includesa base material formed of an oxide such as alumina Al₂O₃ and includingrare metal such as platinum Pt and an NOx absorbing component carried ona surface of the base material; the rare metal serves as a catalyticcomponent. The NOx absorbing component contains at least one selectedfrom, for example, alkali metals such as potassium K, sodium Na, lithiumLi, and cesium Cs, alkali earths such as barium Ba and calcium Ca, andrare earths such as lanthanum La and yttrium Y. In addition, the NOxcatalytic converter 26 may be a selective catalytic reduction (SCR) NOxconverter.

In addition to the oxidizing catalytic converter 6 and the NOx converter26, a particulate filter (DPF) may be provided which collectsparticulates (PM) in the exhaust such as soot. Preferably, the DPF is ofcontinuous regeneration type that continuously oxidizes and combustscollected particulates. Preferably, the DPF is located at leastdownstream of the oxidizing catalytic converter 6 and upstream ordownstream of the NOx catalytic converter 26. For a spark ignitioninternal combustion engine, a three-way catalyst is preferably providedin the exhaust passage. The oxidizing catalytic converter 6, the NOxcatalytic converter 26, the DPF, and the three-way catalyst correspondto an exhaust treatment apparatus according to the present invention.

In the exhaust pipe 3, a burner apparatus 30 is located upstream of theoxidizing catalytic converter 6. The burner apparatus 30 includes a fueladdition valve 7, a glow plug 21 serving as ignition means, and apretreatment catalytic converter 8. The burner apparatus 30 is locateddownstream of a collector portion of an exhaust manifold (not shown inthe drawings) connected to the engine main body 1.

As shown in FIG. 2 and FIG. 3 in detail, the fuel addition valve 7allows a liquid fuel (light oil) to be added into the exhaust. The fueladdition valve 7 includes a single nozzle 7 a. The central axis of thenozzle 7 a contains a component traversing the exhaust pipe 3 and isinclined obliquely downward toward the downstream side of the exhaustpipe 3. Alternatively, a plurality of nozzles maybe provided.

A pretreatment catalytic converter 8 that reforms fuel injected throughthe fuel addition valve 7 is provided between the fuel addition valve 7and the oxidizing catalytic converter 6 in the exhaust pipe 3. Thepretreatment catalytic converter 8 can be configured as an oxidizingcatalytic converter including, for example, a carrier made of zeoliteand carrying rhodium or the like.

When fuel is fed to the pretreatment catalytic converter 8, if thepretreatment catalytic converter 8 has been activated, then the fuel isoxidized in the pretreatment catalytic converter 8. The resultingoxidizing reaction heat raises the temperature of the pretreatmentcatalytic converter 8. This enables an increase in the temperature ofexhaust gas passing through the pretreatment catalytic converter 8.

Furthermore, when the temperature of the pretreatment catalyticconverter 8 increases, hydrocarbons in the fuel which have a largecarbon number are decomposed into reactive hydrocarbons with a smallercarbon number. This allows the fuel to be reformed into reactive fuel.

In other words, the pretreatment catalytic converter 8, on one hand,forms a rapid heater that generates heat rapidly, and on the other hand,forms a reformed fuel discharger that discharges the reformed fuel.Furthermore, a portion or all of the fuel fed through the fuel additionvalve 7 is ignited by the glow plug 21. This also facilitates a rise inthe temperature of exhaust gas.

The pretreatment catalytic converter 8 has an outer diameter smallerthan the inner diameter of the exhaust pipe 3. Thus, when thepretreatment catalytic converter 8 is placed in the exhaust pipe 3,exhaust can pass through a catalyst bypass circuit 3 a that is a gapbetween an outer peripheral surface f the pretreatment catalyticconverter 8 and an inner peripheral surface of the exhaust pipe 3. Thepretreatment catalytic converter 8 is of what is called a straight flowtype in which individual cells communicate with one another fromupstream side to the downstream side. The pretreatment catalyticconverter 8 is arranged in a generally cylindrical outer frame 8 a thatis supported in the exhaust pipe 3 by a plurality of generally radiallyarranged stays 8 b. The pretreatment catalytic converter 8 is enclosedby the catalyst bypass circuit 3 a substantially all around thecircumference thereof except for portions thereof to which the stays 8 bare attached.

The exhaust pipe 3 is generally cylindrically formed. The axis of thedirection of an exhaust flow in the pretreatment catalytic converter 8is located lower, in FIG. 2 and FIG. 3, than the axis of the directionof an exhaust flow in the exhaust pipe 3. Thus, the catalyst bypasscircuit 3 a includes a wide-side bypass circuit 3 b shown in the upperpart of FIG. 2 and FIG. 3 and a narrow-side bypass circuit 3 c shown inthe lower part of FIG. 2 and FIG. 3.

The glow plug 21 is installed such that a heating section 21 a thereofis positioned downstream of the fuel addition valve 7 and upstream ofthe pretreatment catalytic converter 8. The glow plug 21 is connected toan onboard DC power source via a booster circuit (not shown in thedrawings). The heating section 21 a generates heat when current isapplied to the glow plug 21. The heat generated by the heating section21 a enables the fuel fed through the fuel addition valve 7 to beignited to generate a flame F. The glow plug 21 has an axis inclinedtoward the upstream side of the exhaust pipe 3. However, the glow plug21 may be arranged in any orientation, for example, orthogonally to thedirection of a flow or parallel to a longitudinal direction of an impactplate 20 described below. The ignition means may be another apparatussuch as a ceramic heater or a spark plug, particularly an electrothermalapparatus or a spark ignition apparatus.

A lower part of a front end of the outer frame 8 a with the pretreatmentcatalytic converter 8 accommodated therein forms a gutter-likeprojecting portion 8 c that projects toward the upstream side. Theimpact plate 20, which is formed of a flat plate, is fixed to a leadingend (upstream end) and upper end of the projecting portion 8 c. Theimpact plate 20 is slightly inclined so as to lie below the axis of theexhaust pipe 3 and so that a downstream end of the impact plate 20 ispositioned below the upstream end thereof.

The impact plate 20 can be formed of a material such s SUS which hashigh heat resistance and high impact resistance. The fuel addition valve7 allows fuel to be injected obliquely backward and downward toward theimpact plate 20. The central axis of the nozzle 7 a of the fuel additionvalve 7 lies toward the center 20 a of top surface of the impact plate20. The trajectory of the fuel fed through the fuel addition valve 7contains a component acting in a direction traversing the exhaust pipe3. Upon impacting the impact plate 20, the fuel is more smoothlyatomized and more appropriately dispersed and diffused. The fuel havingimpacted the impact plate 20 is directed toward the downstream side byan exhaust flow. The fuel having impacted the impact plate 20 is fed tothe pretreatment catalytic converter 8 and the heating section 21 a ofthe glow plug 21.

The heating section 21 a of the glow plug 21 is located in the vicinityof the pretreatment catalytic converter 8 and slightly upstream of andabove a front end surface of the pretreatment catalytic converter 8 soas to be capable of exchanging heat with pretreatment catalyticconverter 8. That is, the glow plug 21 is positioned such that when thetemperature of the pretreatment catalytic converter 8 rises, theresulting heat radiation and convection serves to raise the temperatureof vicinity of the heating section 21 a of the glow plug 21, thusfacilitating the ignition of the fuel fed through the fuel additionvalve 7. However, the position of the heating section 21 a of the glowplug 21 in the flow direction may be the same as the position of thefront end surface of the pretreatment catalytic converter 8 or aposition located downstream of the front end surface.

As shown in FIG. 1, the engine main body 1 includes an electroniccontrol unit (hereinafter referred to as an ECU) 10 that controlsvarious devices according to the operating status of the engine mainbody 1, a driver's request, or the like. The ECU 10 includes a CPU thatcarries out various arithmetic processes for engine control, a ROM thatstores programs and data required for the control, a RAM thattemporarily stores the results of calculations carried out by the CPU,and an input/output port through which the ECT 10 outputs and receivessignals to and from an external apparatus.

The ECU 10 connects, via electric wires, not only to the above-describedair flow meter 4 but also to various sensors including a crank anglesensor 24 that detects the crank angle of the engine main body 1 and anaccelerator opening sensor 25 that outputs electric signals depending onthe opening of the accelerator. Output signals from the sensors areinput to the ECU 10. Furthermore, the ECU 10 further connects, viaelectric wires, to various devices including the intra-cylinderinjection valve 9, the fuel addition valve 7, and the glow plug 21. Thedevices are controlled by the ECU 10. The ECU 10 can detect the amountof intake air based on the output value from the air flow meter 4,detect the number of engine rotations based on the output value from thecrank angle sensor 24, and detect a demand load on the engine main body1 based on the output value from the output value from the acceleratoropening sensor 25.

The engine main body 1 further includes an intake side valve timingvarying mechanism 41 and an exhaust side valve timing varying mechanism42 which vary valve timings for the intake valve and exhaust valve,respectively, of each cylinder. The varying mechanisms 41 and 42 varythe relative phases of an intake cam shaft 43 and an exhaust camshaft44, respectively, with respect to a crank shaft to vary the opening andclosing timings for the intake valve and the exhaust valve with the sameworking angle maintained. These varying mechanisms 41 and 42 areincluded in the various devices and controlled by the ECU 10.

According to the present embodiment, when temperature rise control isperformed using the burner apparatus 30, the ECU 10 controls the fueladdition valve 7 and the glow plug 21. That is, fuel is injected throughthe fuel injection valve 7, and current is applied to the glow plug 21as necessary to heat the glow plug 21 to a sufficiently hightemperature. The injected fuel is ignited and combusted by the glow plug21 to generate a flame F and thus hot heated gas. The heated gas is fedto the oxidizing catalytic converter 6 and the NOx catalytic converter26. Furthermore, the flame F or heated gas can be utilized to combustreformed fuel discharged through an outlet of the pretreatment catalyticconverter 8.

The amount of fuel injected through the fuel addition valve 7 is setbased on parameters indicative of the operating status of the engine(the parameters include the number of engine rotations, the acceleratoropening, and the amount of intake air) in accordance with a mappre-stored in the ROM of the ECU 10.

As described above, the ignition performance of the burner apparatus 30tends to be degraded when the flow rate of exhaust gas passing throughthe burner apparatus 30 increases to or beyond a predetermined value.This is because at the increased flow rate, the exhaust gas may blow outthe flame, making the ignition difficult.

Such a flame blow-out phenomenon may occur, for example, when the flowrate of the exhaust gas increases to or beyond 12 g/s.

Thus, to deal with this, the present embodiment controls the valvedriving state of at least one of the intake valve and the exhaust valveso as to reduce the flow rate of exhaust gas passing through the burnerapparatus 30 when the flow rate of the exhaust gas is equal to or largerthan a predetermined value. When the valve driving state is thuscontrolled so as to reduce the flow rate of the exhaust gas passingthrough the burner apparatus 30, possible flame blow-out can beprevented or suppressed to ensure sufficient ignition performance.

More specifically, the exhaust-side valve timing varying mechanism 42 iscontrolled such that the exhaust valve is kept open until during adescent of the piston after the end of an exhaust stroke, when the flowrate of the exhaust gas passing through the burner apparatus 30 is equalto or larger than the predetermined value.

As shown in FIG. 4, when the exhaust valve 13 is kept open until duringthe descent of the piston 12 after the end of the exhaust stroke (thatis, the exhaust valve 13 is closed in a delayed manner), a negativepressure generated during the descent of the piston can be utilized tosuck the exhaust gas back into the combustion chamber 14 (that is, tocarry out internal EGR). This enables a reduction in the flow rate ofexhaust gas fed to the exhaust pipe 3 and thus the burner apparatus 30.Hence, even when the flow rate of the exhaust gas increases to or beyondthe predetermined value, the increased flow rate of the exhaust gas canbe reduced to prevent or suppress possible flame blow-out. As a result,appropriate and sufficient ignition performance can be ensured. In FIG.4, the intake valve is shown by reference numeral 15. An intake portthat is in communication with the intake pipe 2 is shown by referencenumeral 16. An exhaust port that is in communication with the exhaustpipe 3 is shown by reference numeral 17.

The flow rate of the exhaust gas can be detected directly by the sensor,but the amount of intake air Ga is preferably used as a substitute valuefor the flow rate of the exhaust gas and detected by the air flow meter4 and the ECU 10. The ECU 10 controls the exhaust-side valve timingvarying mechanism 42 so as to close the exhaust valve 13 (specifically,to end closing the exhaust valve 13) at a predetermined first timingduring the descent of the piston after the end of the exhaust stroke,when the amount of intake air Ga detected using the air flow meter 4 isequal to or larger than a predetermined value (for example, 12 g/s).This keeps the exhaust valve 13 open from before an exhaust top deadcenter to the first timing after the exhaust top dead center. On theother hand, when the amount of intake air Ga detected using the air flowmeter 4 is smaller than the predetermined value, the ECU 10 controls theexhaust-side valve timing varying mechanism 42 so as to close theexhaust valve 13 at a predetermined second timing that is earlier thanthe first timing.

Now, another embodiment will be described. This embodiment issubstantially the same as the above-described embodiment, and mainlydifferences from the above-described embodiment will be described.

The another embodiment includes a halting mechanism adapted to haltoperation of at least one of the intake valve 15 and the exhaust valve13 in a part (certain number) of the plurality of cylinders as shown inFIG. 5. According to the present embodiment, the halting mechanismincludes an intake-side halting mechanism 18 provided for the intakevalve 15 in each of halt-enabled cylinders corresponding to the part ofcylinders and an exhaust-side halting mechanism 19 provided for theexhaust valve 13 in each halt-enabled cylinder. The intake-side haltingmechanism 18 and the exhaust-side halting mechanism 19 are provided ineach of the halt-enabled cylinders and individually controlled by theECU 10.

Various well-known mechanisms maybe adopted as the halting mechanisms 18and 19. For example, the following may be adopted: a mechanism thatselectively makes a cam on a camshaft free by hydraulic control or thelike or a mechanism that selectively precludes, by hydraulic control orthe like, a driving force from being transmitted from the camshaft tothe valve. Alternatively, an electromagnetic driving valve may be usedwhich can be electrically inactivated. The present embodiment includesthe valve timing varying mechanisms 41 and 42 in addition to the haltingmechanisms 18 and 19. However, the valve timing varying mechanisms 41and 42 may be omitted. Any number of halt-enabled cylinders may beplaced at any positions. In each halt-enabled cylinder, one of theintake-side halting mechanism 18 and the exhaust-side halting mechanism19 may be exclusively provided.

The present embodiment controls the intake-side halting mechanism 18 andthe exhaust-side halting mechanism 19 so as to halt operations of boththe intake valve 15 and the exhaust valve 13 in each halt-enabledcylinder as shown in FIG. 5 when the flow rate of exhaust gas passingthrough the burner apparatus 30 is equal to or larger than apredetermined value. In the halt state, the intake valve 15 and theexhaust valve 13 are kept closed. Of course, during a halt, no fuel isinjected through the intra-cylinder fuel injection valve 9 (omitted fromFIG. 5). During a halt, either the intake valve 15 or the exhaust valve13 may be exclusively halted. In short, the communication between theintake port 16 or the intake pipe 2 and the exhaust port 17 or theexhaust pipe 3 may be disrupted.

When the operation of the at least one of the intake valve 15 and theexhaust valve 13 in each halt-enabled cylinder is halted as describedabove, no exhaust gas is fed from the halt-enabled cylinder toward theexhaust pipe or the burner apparatus 30. This enables a reduction in thetotal flow rate of exhaust gas from all the cylinders. Even when theflow rate of the exhaust gas increases to or beyond the predeterminedvalue, the increased flow rate can be reduced. Hence, possible flameblow-out can be prevented or suppressed to ensure appropriate andsufficient ignition performance.

As described above, the flow rate of the exhaust gas can be detecteddirectly by the sensor, but the amount of intake air Ga is preferablyused as a substitute value for the flow rate of the exhaust gas anddetected by the air flow meter 4 and the ECU 10. The ECU 10 controls theintake-side halting mechanism 18 and the exhaust-side halting mechanism19 so as to halt the operations of both the intake valve 15 and theexhaust valve 13 in each halt-enabled cylinder when the amount of intakeair Ga detected using the air flow meter 4 is equal to or larger than apredetermined value (for example, 12 g/s). This sets the halt-enabledcylinders to a halt state, while setting the other cylinders (normalcylinders) to an operative state. On the other hand, the ECU 10 controlsthe intake-side halting mechanism 18 and the exhaust-side haltingmechanism 19 so as to operate both the intake valve 15 and the exhaustvalve 13 in each halt-enabled cylinder, when the amount of intake air Gadetected using the air flow meter 4 is smaller than a predeterminedvalue. This makes both the halt-enabled cylinders and the normalcylinders operative.

The present invention has been somewhat specifically described. However,it should be noted various alterations and changes may be made to theclaimed invention without departing from the spirit and scope of theinvention. The embodiments of the present invention are not limited tothose which are described above. The present invention includes anyvariations and applications embraced in the concepts of the presentinvention defined by the claims. Thus, the present invention should notbe interpreted in a limited manner but is applicable to any othertechniques included within the scope of the concepts of the presentinvention. Means for solving the problems according to the presentinvention may be combined together wherever possible.

At least one of the pretreatment catalytic converter and the exhaustpipe may have a noncircular cross section such as a rectangular crosssection or an oblong cross section. The types and arrangement sequenceof the components of the exhaust treatment apparatus which are presentdownstream of the pretreatment catalytic converter are optional.

1. An internal combustion engine comprising: an exhaust treatmentapparatus provided in an exhaust passage; a burner apparatus providedupstream of the exhaust treatment apparatus to raise exhausttemperature, and valve driving control unit for controlling a valvedriving state of at least one of an intake valve and an exhaust valve soas to reduce a flow rate of exhaust gas passing through the burnerapparatus when the flow rate of the exhaust gas is equal to or largerthan a predetermined value.
 2. The internal combustion engine accordingto claim 1, wherein the valve driving control unit comprises: a valvetiming varying mechanism adapted to vary a valve timing for the exhaustvalve, and first control unit programmed to control the valve timingvarying mechanism in such a manner that the exhaust valve is kept openuntil during a descent of a piston after end of an exhaust stroke, whenthe flow rate of the exhaust gas is equal to or larger than thepredetermined value.
 3. The internal combustion engine according toclaim 1, wherein the valve driving control unit comprises: a haltingmechanism adapted to halt operation of at least one of the intake valveand the exhaust valve in a part of a plurality of cylinders; and secondcontrol unit programmed to control the halting mechanism so as to haltthe operation of at least one of the intake valve and the exhaust valvein the part of cylinders, when the flow rate of the exhaust gas is equalto or larger than the predetermined value.
 4. The internal combustionengine according to claim 1, further comprising detection unit fordetecting an amount of intake air as a substitute value for the flowrate of the exhaust gas, and wherein the valve driving control unitcontrols the valve driving state of at least one of the intake valve andthe exhaust valve so as to reduce the flow rate of the exhaust gas whenthe amount of intake air detected by the detection unit is equal to orlarger than a predetermined value.
 5. The internal combustion engineaccording to claim 1, wherein the burner apparatus comprises a fueladdition valve, ignition unit, and a pretreatment catalytic converter.